Synkinesis vesicles

An electron donor or acceptor site is usually needed in organic synthons for covalent synthesis. The covalent connection of both leads to a new molecule in an essentially irreversible synthetic reaction. Organic synkinons for non-covalent synkinesis usually contain a hydrophilic and a hydrophobic part and/or proton donor or acceptor sites. Non-covalent connection of such amphiphiles leads to a molecular assembly in a reversible synkinetic reaction. Amphiphiles are not only surface active molecules ( surfactant, detergent ), but much more important, they create surfaces. This becomes particularly evident in microemulsions and in suspensions of vesicles and micellar fibres, but is also true in nanoholes and pores, on monolayer surfaces and for many other supramolecular structures. 

There are, for example synkinons for the synkinesis of micelles, vesicles, pores, fibres and planar mono- or multilayers. A given synkinon can also be applied for another synkinetic target if the conditions are changed or if the synkinon is chemically modified. The most simple example is stearic acid. At pH 9, it is relatively well-soluble in water and forms spherical micelles. If provided with a hydrogen bonding chiral centre in the hydrophobic chains (12-hydroxystearic acid), it does not only form spherical micelles in water but also assembles into helical fibres in toluene. At pH 4, stearic acid becomes water-insoluble but does not immediately crystallize out spherical vesicles form. A second type of synkinon, which produces perfectly unsymmetrical vesicle membranes, consists of bolaamphiphiles with two dififerent head groups on both ends of a hydrophobic core. Such bolaamphiphiles are also particularly suitable for the stepwise construction of planar multilayered assemblies. 

The great diversity of concepts and synkinetic structures which have been realized within the last decade and which is partly represented in this volume, suggests that all kinds of membranes are accessible asymmetric, as thin as 2.0 nm, helical, porous, fluid or solid, chiral on the surface or in the centre, photoreactive etc. etc. This diversity will inevitably grow. A few obvious unsolved problems which need immediate attention can also be detailed e.g. synkinesis of solid micelles and vesicles from concave molecules with at least four hydrogen bonding sites, co-crystallization of porphyrins with solid membrane structures, and evaluation of nanopores as catalytic sites. Many more such target assemblies will undoubtedly be envisioned and successfully syn-kinetized. 

The other chapters then lead from the simple to the more complex molecular assemblies. Syntheses of simple synkinons are described at first. Micelles made of 10-100 molecules follow in chapter three. It is attempted to show how structurally ill-defined assemblies can be most useful to isolate single and pairs of molecules and that micelles may produce very dynamic reaction systems. A short introduction to covalent micelles, which actually are out of the scope of this book, as well as the discussion of rigid amphiphiles indicate where molecular assembly chemistry should aim at, namely the synkinesis of solid spherical assemblies. Chapter four dealing with vesicles concentrates on asymmetric monolayer membranes and the perforation of membranes with pores and transport systems. The regioselective dissolution of porphyrins and steroids, and some polymerization and photo reactions within vesicle membranes are also described in order to characterize dynamic assemblies. 

Typical target assemblies of synkinesis are noncovalent dimers, charge-transfer complexes, hetero-dimers and -trimers, cyclic or helical oligomers, inherently asymmetrical or helical membranes in the form of vesicles, spheres, tubules, and rods, as well as macroscopic surface monolayers. Pores and domains in vesicle membranes and gaps of molecular size in surface monolayers are other synkinetic targets. They may function as receptors or reactive, enzyme-like surface clefts (Fendler, 1982 Fuhrhop 1982 Israelaehvili, 1992 Fuhrhop and Koning). 

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